Heat-capacity measurements by adiabatic calorimetry at temperature T = 5 K to 350 K were supplemented by differential-scanning calorimetry (d.s.c.) into the liquid region on thallium(I) propanoate and pentanoate. Apparent phase transitions were noted for the propanoate for the crystal III-to-crystal II transition with [Delta]transSom = (1.473+/-0.001)R at T = (277.7+/-0.1) K adiabatic calorimetry and for the crystal II-to-crystal I transition at (0.10+/-0.01)R at T = (268.4+/-0.4) K by d.s.c. and for the crystal I-to-liquid transition with [Delta]trsSom = (2.70+/-0.09) R at T = (468.0+/-0.4) K. For the VI-to-V and V-to-IV transitions of the pentanoate by adiabatic calorimetry the corresponding values are (0.359+/-0.002)R and (235.1+/-0.1) K, (1.511+/-0.003)R and (219.3+/-1) K. For the IV-to-III, III-to-II, II-to-I, plus crystal I-to-mesophase and mesophase-to-isotropic liquid for the same compound the pairs of values by d.s.c. (only) are: (0.26+/-0.02)R and (234.6+/-0.4) K; (1.00+/-0.04)R and (284.5+/-0.4) K; (0.72+/-0.03)R and (353.0+/-0.4) K; (1.50+/-0.05)R and (455.0+/-0.5) K; and (0.75+/-0.04)R and (488.0 +/-0.8) K. Like thallium(I) butanoate, the propanoate does not show a mesotropic liquid phase.Supported in part by the National Science Foundation. Partial support of this research by the CICYT of the Spanish Ministerio de Educación y Ciencia (Grant in aid for scientific research PB88-127) is gratefully acknowledged.Peer reviewed